Monday, January 10, 2011

Automatic Voice Relay System

One of the reasons why I have not been an enthusiast of the D-Star system is that it creates a separate class of activity incompatible with existing voice modes just for the dubious benefit (from an amateur point of view) of using digital voice instead of analogue. Using EchoLink, IRLP and APRS we already have a global network that allows one ham to contact another anywhere in the world using ham radio, one that does not require anyone to purchase expensive new equipment from Icom or anyone else. What we have not done is put it together in a way that makes it work seamlessly as a coherent network.

Automatic Voice Relay System (AVRS) is an idea by Bob Bruninga, WB4APR, the inventor of APRS, first published in 2000, to create a system that allows users of EchoLink, IRLP and even D-Star to inter-communicate. APRS provides the location and identification information for the analogue FM EchoLink and IRLP users, something that is already built in to the D-Star system. As is often the case, those who have the great ideas don't always have the skills needed to bring them to fruition, so AVRS remained little more than an idea for ten years.

Now, apparently, a developer has been found who is able and willing to write the software that will enable AVRS version 2 to come into being. You can read more about AVRS here. For seamless one-button operation you will need one of the new generation of APRS-capable radios (Kenwood TM-D710, TH-D72 or Yaesu FTM-350) that are able to QSY to a frequency contained in an APRS packet. Some will argue that if you are going to buy one of those, why not buy a D-Star radio instead? But AVRS capability, being based on APRS, can easily and inexpensively be added to any analogue FM radio. AVRS will not leave analogue FM users out in the cold because their local repeater converted to D-Star, as has happened in some parts of Britain.

One of the interesting aspects of AVRS version 2 is the development of A-Star repeaters. These are analogue FM repeaters with a D-Star gateway that use the D-Star network to link them together. Callsign and location (if known) information is transmitted as a 0.3sec APRS packet burst at the end of each over. A-Star users will appear to D-Star users just like other D-Star users and can easily intercommunicate. A-Star users can initiate a contact with another A-Star or D-Star user just by sending an APRS message starting with A*. A-Star users don't even need to be monitoring a repeater in order to be contactable: they will receive the message as an ordinary APRS message and can QSY to the repeater (with one button press if using one of the radios mentioned above) using the information contained in it.

AVRS looks like a great idea with the potential to bring digital and analogue voice users together. It might even erode some of the analogue vs D-Star conflict.
Post a Comment